1. Field of the Invention
The present invention relates generally to the manufacture of integrated optical devices (IOCS) for use in optical communications networks and optical computing devices, and more particularly to a method for manufacturing integrated optical devices on a planar substrate using ultraviolet light.
2. Description of the Prior Art
The explosive growth of telecommunication and computer communications, especially in the area of the Internet, has created a dramatic increase in the volume of worldwide data traffic which has caused an increasing demand for communication networks providing increased bandwidth. To meet this demand, fiber optic communication systems have been developed to harness the enormous usable bandwidth (tens of tera-Hertz) of a single optical fiber transmission link.
Because it is not possible to exploit all of the bandwidth of an optical fiber using a single high capacity channel, wavelength division-multiplexing (WDM) fiber optic systems have been developed to provide transmission of multi-carrier signals over a single optical fiber thereby channelizing the bandwidth of the fiber. In accordance with WDM technology, a plurality of superimposed concurrent signals are transmitted on a single fiber, each signal having a different wavelength. WDM technology takes advantage of the relative ease of signal manipulation in the wavelength, or optical frequency domain as opposed to the time domain. In WDM networks, optical transmitters and receivers are tuned to transmit and receive on a specific wavelength, and many signals operating on distinct wavelengths share a single fiber.
Wavelength multiplexing devices are commonly used in fiber optic communication systems to generate a single multi-carrier main communication signal stream in response to a plurality of concurrent signals having different wavelengths, for transmission via a single fiber. Wavelength demultiplexing devices are commonly used to separate the composite wavelength signal into the several original signals having different wavelengths.
The transmission capacity of an optical network is proportional to the number of channels carried by the main communication signal stream in the optical network. Dense wavelength division multiplexing (DWDM) systems provide many channels with narrowly spaced wavelength separations, such as 50 or 100 GHz channel spacing which corresponds to a wavelength separation of 0.4 nm and 0.8 nm respectively. The number of channels deployed in WDM optical networks is continually increasing. Currently, it is common for WDM optical networks to deploy 16, 32, and 40 channels. DWDM systems providing very large number of channels (e.g., 80 and 160 channels) are likely to be deployed in the foreseeable future.
In optical networks having a large number of channels, a great number of different types of optical components are used to manipulate optical signals. For example, various optical components are used to generate, transmit, stabilize, attenuate, amplify, switch, combine or receive optical signals. There has been a high demand for many optical network components for the last several years and demand continues to exceed supply. One reason for the lack of availability of many optical components is that many of today""s component technologies are based on discrete or xe2x80x98bulkxe2x80x99 component technologies. Discrete optical components are bulky, and are either hard to manufacture or difficult to install, or both. Discrete components cannot integrate multiple functions in a single package.
Most of these traditional optical components are either manufactured with high labor costs, or have low manufacturing yields that are typically lower than 50%. Moreover, automated manufacturing for these type of components is difficult to achieve, and therefore not widely deployed. The currently used processes rely primarily on manual labor. Some of the manually manufactured discrete components are unable to economically support more than 40 channels or unable to economically support data rates of 10 Gbit/sec. These manually manufactured optical components have high insertion loss or high dispersion, and are unable to support a dynamic wavelength environment, i.e., they are non-tunable. Furthermore, these components cannot support higher levels of component integration.
As the development and expansion of applications for optical networking equipment increases, and as the number of channels deployed in WDM optical networks increases, it becomes necessary to manufacture optical components at lower cost and, more importantly, at a higher level of component function integration.
Integrated Optical Components (IOCs) are optical components that are made in or within optical materials or substrates that can pass light signals. Examples of IOCs include light passages or waveguides for guiding, transmitting, manipulating, or even amplifying light signals. In order to implement the next generation of optical networking systems, it is necessary to be able to reliably manufacture large quantities of IOC""s, such as integrated optical couplers, integrated attenuators, integrated waveguides, integrated switches, integrated wavelength lockers, integrated isolators, integrated amplifiers, integrated gratings, integrated polarizers, or integrated components combining two or more functions.
One could compare discrete optical components with individual transistors. It is hard to imagine a modern personal computer containing tens of thousands of individual transistors. Integrated optical components (IOC) act as an optical equivalent to integrated circuits. IOCs will solve most of, if not all, the aforementioned drawbacks in the optical networking applications.
Semiconductor manufacturing processes are not suitable for the manufacture of IOCs. Using such processes to manufacture IOCs would be expensive, difficult to mature, and result in low yields. Furthermore, hundreds of millions of dollars would be required to develop such processes to produce prototype IOCs. Equipment for mass production of Integrated Optical Components based on traditional semiconductor processes would cost billions of dollars.
It is known that exposing doped glass to intense ultraviolet light can change the refraction properties of the glass. FIGS. 1A through 1C illustrate the effects of exposing an area of a doped glass to intense ultraviolet light. FIG. 1A shows a prior art method at 10 for focusing a deep ultraviolet laser beam 12 onto glass material (not shown) via a lens 14 in order to increase the refraction index of a portion of the glass material disposed beneath a focal point 16. The refraction index of optical glass can be permanently affected by exposure to light of a selected wavelength and intensity, depending on the specific composition of the glass. The size of the focal point 16 is dependent on the size of the area illuminated by laser light, the focal length of the lens 14 and the wavelength of the laser beam. The use of a shorter wavelength laser beam 12 results in a smaller focal point 16. A well designed lens system and a deep ultraviolet laser source, such as a commercially available 248 nm or 193 nm wavelength excimer laser, could be used to produce a spot size of 0.25 xcexcm or even 0.18 xcexcm.
FIG. 1B shows a top view of a region of glass material at 18 exposed to deep ultraviolet radiation disposed beneath the focal spot. A center portion 20 of the exposed region receives the highest intensity ultraviolet radiation, while a first perimeter portion 22 receives a lower intensity of radiation from the laser beam 12 (FIG. 1).
FIG. 1C shows the refraction index distribution at 24 across the exposed glass region 18 (FIG. 1B). As shown the refraction index of the center portion 20 of the exposed region is greatly increased over the refraction index of the surrounding glass.
What is needed is an inexpensive process for fabricating integrated optical components, each having many different functions in a single component.
What is also needed is a process for fabricating integrated optical components with low insertion loss and good device flexibility that is suitable for automated manufacture and large volume of production.
Further needed is a process for fabricating integrated optical components that requires fewer manufacturing steps and less equipment.
It is therefore an object of the present invention to provide an inexpensive process for fabricating integrated optical components, each having many different functions in a single component.
Another object of the present invention to provide a process for fabricating integrated optical components with low insertion loss and good device flexibility that is suitable for automated manufacture and large volume of production.
Yet another object of the present invention is to provide a process for fabricating integrated optical components that requires fewer manufacturing steps and less equipment.
Briefly, a presently preferred embodiment of the present invention provides a process for forming an integrated optical device in a glass substrate, including the steps of: providing a glass substrate having a base index of refraction; providing a UV light beam; focusing the beam onto a portion of the glass substrate in order to form a region of increased refraction; and scanning an elongated region of the glass substrate with the beam in order to define at least one elongated optical channel having an increased index of refraction relative to the base index of refraction, the elongated optical channel for guiding light transmitted there along.
The process further includes a step of forming a plurality of elongated optical channels in the glass substrate, wherein a first optical channel guides light toward the plurality of elongated optical channels such that the guided light is divided among the plurality of elongated optical channels, thereby forming an optical beamsplitter.
An important advantage of the method of the present invention is that it provides the capability to manufacture integrated optical components at lower cost and higher repeatability, and allows the manufacturing of components with greater functional integration than prior art methods.